This invention relates to apparatus for developing one face of photosensitive sheet or strip stock, of the type having a metering roller for the metered supply of developer liquid to an applicator roller, a profiled roller for pressing the stock against the applicator roller, as well as guide means for feeding and guiding the stock.
The invention relates particularly to apparatus for moistening one side of sheets or of paper strips.
Prior art apparatus of this kind is utilized in copying equipment, for example, in which it is intended for developing diazotypes.
Apparatus of this type is diagrammatically depicted and described in U.S. Pat. No. 4,068,620. It contains a metering roller made of a metal core surrounded by a plastic sheath. The sheath is provided with fine, helical grooves. The metering roller transfers liquid developer to an applicator roller consisting of a metal core and a smooth rubber sheath. Pressing against the applicator roller is a profiled roller comprising a metal core and a sheath of profiled rings ranged side by side. Each of the profiled rings has outwardly projecting profiles on its outside surface, preferably pyramid-shaped points, regularly distributed over the circumference and repeated n times. Each two adjoining rings are twisted by a certain angle relative to one another.
By means of the profiled roller utilized in this apparatus, it is intended to press the diazo paper uniformly against the applicator roller, the surface of the profiled roller having to remain as dry as possible in the absence of copy stock so that moistening of the back of a copy to be developed can be prevented.
It is proposed to make the profile rings of plastic or metal. The pyramid-shaped points are relatively hard and non-elastic.
In U.S. Pat. No. 4,135,475, reference is made to difficulties which arise with the aforementioned profiled roller. With very wide copiers which are customarily used for making diazotypes, because of sagging of the rollers, the forces acting upon the copy to be developed are not uniform over the entire length of the nip between the applicator roller and the profiled roller. Even small differences in the amount of liquid developer applied to the diazo layer cause fairly great differences in color intensity in the developed copy. Well developed locations alternate with locations developed weakly or not at all. In order to eliminate this problem, it is proposed to divide the profiled roller into a number of partial rollers joined to one another by connection elements in such a way that adjacent partial rollers are displaceable radially to one another. Associated with each partial roller is a spring element intended to press the partial roller against the applicator roller.
A drawback of this second prior art apparatus is the relatively complicated and expensive design, as well as the fact that between the individual partial rollers, where the spring elements engage, there are gaps in which the copy stock is not pressed against the applicator roller. The formation of streaks on the developed copy is possible.